--- a/hgext/purge.py	Mon Jun 21 17:29:22 2021 +0200
+++ b/hgext/purge.py	Tue Jun 22 13:18:29 2021 -0400
@@ -30,3 +30,9 @@
 
 # This empty extension looks pointless, but core mercurial checks if it's loaded
 # to implement the slightly different behavior documented above.
+
+# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = b'ships-with-hg-core'